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  Dc current regulator insensitive to conducted emiDc current regulator insensitive to conducted emi description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070216484, Dc current regulator insensitive to conducted emi. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] This invention relates to DC current regulators and to current mirrors and to methods of operating the same. BACKGROUND TO THE INVENTION [0002] The phenomenon of electromagnetic interference (EMI) and the resulting general framework defining to what extent electronic devices and applications must be able to work together without disturbing each other (electromagnetic compatibility, abbreviated EMC) first became a concern during the second World War. One of the top EMI nuisances at that time was the electric motor noise, conducted through power supply lines into sensitive electronic equipment. Since then, the major increase of electronic appliances, the use of higher frequencies and the omnipresence of (fast) switching digital computing devices have made EMC a global concern, that has gained much importance over the years. With appliances working at speeds of a few hundred megahertz, to some gigahertz, even the tiniest track of the most carefully designed printed circuit board (PCB) behaves like a microwave transmission line. In the same way that increasing working frequencies extrapolated the EMI problem from long power lines to much smaller PCB tracks, history is repeating itself by moving this issue towards the field of micro electronic circuits. Due to their small size, microelectronic circuits are in practice not easily disturbed by radiated disturbances, they are however much more prone to noise conducting interferences, that are present on PCB tracks. Current mirrors and current regulators are two commonly used elements in analog circuitry which can be susceptible to conducted EMI. SUMMARY OF THE INVENTION [0003] Accordingly, an aspect of the present invention seeks to provide a DC current regulator which is affected, to a lesser degree, by conducted EMI. A further aspect of the present invention seeks to provide a current mirror which is affected, to a lesser degree, by conducted EMI. [0004] A first aspect of the present invention provides a current regulator circuit comprising: [0005] a first circuit node which is operable to receive an external input voltage; [0006] a transistor having an input, a first leg and a second leg, the first leg of the transistor being isolated from the first circuit node; [0007] an amplifier having an output connected to the input of the transistor, a first amplifier input for receiving a reference voltage and a second amplifier input connected to the first circuit node; [0008] a low-pass filter connected between the output of the amplifier and the first circuit node; [0009] a current mirror connected in series with the second leg of the transistor and having a first branch for providing a regulated output current and a second branch which connects to the first circuit node. [0010] In this manner, a feedback loop is provided from the first circuit node, the second amplifier input, the output of the amplifier, the input of the transistor, the second leg of the transistor and via the current mirror back to the first circuit node. The loop is subject to the effects of the low-pass filter. The low-pass filter has an advantage of shielding the amplifier and other parts of the circuit from EMI. Isolating the first leg (i.e. the source) of the transistor from the first circuit node, by use of the current mirror, prevents EMI from clipping, and thus distorting, the output current, as occurs in conventional regulators. A further advantage of the improved regulator is that the external EMI source connected to the first circuit node "sees" a high impedance drain (e.g. of an MOS transistor M3 in FIG. 7) instead of a low impedance source, e.g. of an MOS transistor such as M1 in FIG. 1. This also increases the effectiveness of any decoupling capacitor which is connected between the first circuit node and ground. A further advantage is that Ci of the filter can be small, due to the Miller effect of the filter. This makes it advantageous when the circuit is implemented in an integrated circuit, where it is desirable to keep the capacitance as low as possible. A still further advantage is that EMI disturbance is filtered before it reaches the input of the amplifier. A DC shift at the output of the amplifier due to EMI injection at its input is avoided because the signal at the input to the opamp is already filtered by the filter. [0011] Preferably, in the circuit the first branch is directly or indirectly coupled to an output stage, which comprises a further current mirror, wherein the further current mirror is an EMI-filtering current mirror. [0012] This provides the advantage that the output is smoothed still further with respect to EMI frequencies. [0013] A regulated output current can be taken directly from the second leg (drain) of the transistor. In this embodiment, the first branch of the current mirror is in series with the second leg (drain) of the transistor. In an alternative, and preferred, arrangement the first branch of the current mirror which provides the regulated output current is a mirrored branch. This allows the current flowing from the second leg of the transistor to be copied and scaled, as required. In a further alternative embodiment the first mirrored branch connects to an output stage comprising one or more current mirrors which each provide a degree of EMI-filtering. [0014] The amplifier is preferably an operational amplifier (op-amp). [0015] A further aspect of the present invention provides a current regulator circuit comprising: [0016] a first circuit node which is operable to receive an external input voltage; [0017] a transistor having an input, a first leg and a second leg, the first leg of the transistor being connected to the first circuit node; [0018] an amplifier (10) having an output connected to the input of the transistor, a first amplifier input for receiving a reference voltage (VREF) and a second amplifier input connected to the first circuit node; [0019] a low-pass filter connected between the output of the amplifier and the first circuit node; and, [0020] a current mirror connected in series with the second leg of the transistor, wherein the current mirror comprises a second transistor and a third transistor whose gates are connected together at a mirror node, the third transistor having an input branch connected in series with the second leg of the transistor to receive current and the third transistor having an output branch to mirror the received current as an output current (I.sub.ref); [0021] a fourth transistor connected between the mirror node and a supply rail (Vcc); and, Continue reading about Dc current regulator insensitive to conducted emi... Full patent description for Dc current regulator insensitive to conducted emi Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Dc current regulator insensitive to conducted emi patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Dc current regulator insensitive to conducted emi or other areas of interest. ### Previous Patent Application: High linearity and low noise amplifier with continuously variable gain control Next Patent Application: Differential amplifier stage Industry Class: Amplifiers ### FreshPatents.com Support Thank you for viewing the Dc current regulator insensitive to conducted emi patent info. 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